Invertebrates
Stick Insect
Phasmatodea · also called walking stick, phasmid
A stick insect is an animal that has committed entirely to a single idea: be a twig. Its body is shaped like a stem, coloured like bark, and it will sit motionless for hours, swaying gently as if in a breeze, so that a bird looking straight at it sees only a branch. There are around 3,000 species, and one of them is the longest insect in the world.
Overview
Stick insects make up the order Phasmatodea, mainly tropical and subtropical, with the flattened leaf insects as one branch. All are leaf-eaters that feed at night, and most specialise on one or a few food plants. They rely on camouflage for defence, backed up by holding still and swaying. The longest insect on Earth is a stick insect, the Chinese Phryganistria chinensis at over 60 cm with its legs extended.
Females without males
Many stick insects reproduce by parthenogenesis, laying unfertilised eggs that hatch into female clones, and some species have no males at all. This is why a single pet stick insect can found generations on its own. The eggs look like seeds, and in some species carry a fatty knob that ants carry underground, leaving the egg to hatch in safety.
More than camouflage
A cornered stick insect may drop a leg and regrow it, flash bright hindwings, curl its abdomen up like a scorpion as a bluff, or spray an irritating chemical at a predator’s eyes. The heavy Lord Howe Island stick insect, thought extinct after rats reached its island, was rediscovered on a single sea stack in 2001 and is now bred in zoos.
Status
Stick insects as a group are Not Evaluated. Most are common, a few are minor tree pests, and several island endemics are Critically Endangered because of introduced predators.
Stick Insect: common questions
How do stick insects hide so well?
They combine three things. First, their bodies are the right shape, long and thin with legs that fold flat along the body so the whole animal reads as a twig, or in leaf insects broad and flat with leaf-like veins and edges. Second, they are the right colour and texture, brown, green, or grey with bumps, ridges, and even patches that mimic lichen or damage. Third, they behave correctly, staying motionless for long periods, choosing a resting posture that matches the surrounding stems, and often swaying slowly back and forth as if the branch were moving in a breeze, which breaks up the outline that a predator's eye is trying to lock onto. Many species are also active only at night.
Can stick insects reproduce without mating?
Yes, and many do so routinely. A large number of stick insect species can reproduce by parthenogenesis, where a female lays eggs that develop without being fertilised and hatch into more females genetically identical to her. In some species this is the normal method and males are unknown or extremely rare; in others, females mate when they can but will switch to parthenogenesis if no male is available. This is one reason a single stick insect brought into a classroom or kept as a pet can produce generations of offspring on its own, and why escaped or released pet stick insects can establish new populations from a single individual.
Are stick insects good pets, and are they dangerous?
They are among the easiest of all pets to keep, which is why they are so common in schools and homes. They need only a tall, ventilated container, a supply of fresh food plant such as bramble stood in water, light misting for humidity, and warmth, and they do not bite or sting in any way that matters. The main cautions are that a few species can spray a mildly irritating defensive chemical if badly handled, that their eggs and young should never be released outside their native range because parthenogenetic species can become invasive, and that keepers should check which species are legal to keep in their country, as some are restricted as potential plant pests.
Which is the biggest stick insect?
By total length including the outstretched legs, the largest known insect of any kind is a stick insect, Phryganistria chinensis, described from southern China, with a specimen measured at just over 60 cm. Measured by body alone, several giants come close, including Phobaeticus species from Borneo and Malaysia at more than 35 cm of body and around 55 cm with legs extended, and the Australian titan stick insect. The heaviest stick insects are different animals again, the stout, wingless species such as the Lord Howe Island stick insect and some New Guinea phasmids, which can weigh as much as a small bird even though they are not the longest.